Production of high energy fuel



Sept. 17, 1963 c. M. KRON PRODUCTION oF HIGH ENERGY FUEL Filed June 27, 1960 United States Patent O 3,104,266 PRDUCTION F HIGH ENERGY FUEL Carl M. Kran, Houston, Tex., assigner to Phillips Petroleum Company, a corporation of Delaware Filed .lune 27, 1960, Ser. No. 39,146 8 Claims. (Cl. 260-666) This invention relates to the production of a highenergy fuel. In one aspect this invention relates to the production of a high-energy fuel comprising dimethyl bicyclodecanes.

The advent of turbo-jet engines, ram jets, and liquid fuel rocket engines has resulted in the development and commercialization of several grades of -jet fuels most of which are kerosene grade hydrocarbons. The most widely used grade is currently designated as IP-4, although other grades such as LIP-6 have been employed at various times. These relatively lcheap hydrocarbon fuels have, in general, proved to be satisfactory to date, but it would be very desirable if higher density hydrocarbons of essentially the same burning characteristics and having higher heats of combustion were available.

The development of supersonic aircraft with ultra Wing sections has practically eliminated the use of internal wing space for the storage of f-uel. This limitation seriously hampers the range of high speed aircraft since only a certain number of gallons of fuel can be stored in the fuselage. Thus, if higher density hydrocarbons with essentiallly the same heat of combustion in B.t.u.s per pou-nd were available, a tank of `given volume could store many more B.t.u.s and more thrust would be available. lf said higher density fuels also have a higher heat of combustion, then the .gain in thrust is even greater.

Various hydrocarbon fractions o-f petroleum contain large amounts of naphthenic compounds and normal parains. Many of these compounds are relatively useless in their original for-m. However, they can be converted to valuable materials which are useful in motor fuels or as starting materials in chemical processes. Thus, for example, nor-mal hexane which has a low octane number can he converted to isohexanes which have high octane numbers and which 'form valuable components of motor fuels. Also, a compound such as methylcyclopentane can be converted to cyclohexane which is a :starting material in the manufacture of nylon fibers. Commercial processes are available for converting said normal hexane and said methylcyclopentane as described.

ln one commercially available process, a hydrocarbon stream comprising normal hexane and methylcyclopentane is contacted with a metal halide-hydrocarbon complex catalyst in a reaction zone under isomerization conditions whereby at least a portion of said normal hexane is isomerized to isohexanes and at least a portion of said methylcyclopentane is isomerized to cyclohexane. In :said process there are recovered from the hydrocarbon eiiluent from said reaction zone a stream comprising isohexanes, la stream comprising a mixture of unreacted normal hexane and unreacted methylcyclopentane, a stream comprising cyclohexane and a heavy reject stream of higher boilin-g hydrocarbons. It has now been discovered ythat said heavy reject stream contains substantial proportions of dimethyl bicyclodecanes. Said dimethyl bicyolodecanes have heats of combustion in the order of about 138,000

3,104,256 Patented Sept. 17, 1963 fice to about 140,000 B.t.u. per .gallon (gross) and densities of about 0.85 to about 0.89 land are thus excellent high density, high energy fuels `for jet engines and other continuous combustion-type power plants. Said dimethyl bicyclodecanes can be recovered by fractionating said heavy reject stream of higher boiling hydrocarbons.

Thus, in its broadest aspects, the present invention resides in a process for `the production of a high energy fuel comprising dimethyl bicyclodecanes which process comprises, contacting a hydrocarbon feed stream comprising normal hexane and methylcyclopentane in a reaction zone with a metal halide-hydrocarbon complex catalyst under isomerizing conditions whereby at least a portion of said normal hexane is isomen'zed :to isohexanes and at least a portion of said methylcyclopentane is isomerized to cyclohexane; passing hydrocarbon effluent from said reaction zone through a series of fractionation zones to separate a stream comprising isohexanes, a stream comprising a mixture of unreacted normal hexane and unre- -acted methylcyclopentane, a stream comprising cyclohexane and a heavy reject :stream of higher boiling hydrocarbons; and fractionating said heavy reject stream of higher boiling hydrocarbons to recover said high energy fuel comprising dimethyl bicyclodecanes.

In the fractionation of said heavy reject stream, there is also recovered as an overhead stream therefrom a stream comprising cyclohexane, isohe-ptanes, C7 naphthenes, C8 naphthenes, and C9 naphthenes. It has also been -discovered that the yield of said high energy fuel `comprising dimethyl bicyclodecanes can be increased by lrecycling said overhead stream to said reaction zone. Thus, in a more limited embodiment the present invention resides in said process for the production of said high energy fuel, and indicates the additional step of recycling said overhead stream from the fractionation of said reject stream to the reaction zone so as to increase the production of said high energy fuel. It is not essential that the isoheptanes, C, naphthenes, C8 naphthenes, and C9 naphthenes be included in the charge to the reaction zone by recycling said overhead stream. Thus in :another embodiment of the invention said isoheptanes, C7 naphthenes, C8 naphthenes, and C9 naphthenes can Ibe included as a portion of the fresh charge to said reaction zone.

An object of this invention is lto provide an improved process for the conversion of hydrocarbons. Another object of this invention is to provide a process for the production of high energy fuels for jet engines and other continuous combustion-type power plants. Another object of this invention is to provide a process for the production of a high energy fuel comprising dimethyl bicyclodecanes. Another object of this invention is toprovide a process for the production of dimethyl bicyclodecanes. Still another object of this invention is to provide a process for Athe simultaneous production of valuable motor fuel components (isohexanes), valuable raw materials for the lmanufacture of synthetic `fibers (cyclohexane), :and valuable high-density, high-energy yfuel for jet engines and other continuous combustion-type power plants (dimethyl bicyclodecanes). Other aspects, objects and advantages of the invention will be apparent to those skilled in the art in =view of this disclosure.

As used herein and in the claims, unless otherwise specified, the term dimethyl bicvclodecanes is used generically to denote the various dimethyl bicyclodecanes such as:

The somerization of normal hexane and methylcyclopentane according to the method of this invention is usually carried out at a temperature in the range of between about 90 F. and about 160 F., the particular temperature employed being dependent on the composition of the feed stream being charged to the reaction zone. When maximum production of said high energy fuel comprising dimethyl bicyclodecanes is desired, it is preferred to operate within the upper portion of `the above temperature range, erg., from about 150 to about 160 F Said isomerization is preferably carried out under sufficient pressure to provide liquid phase conditions in the reaction zone, namely a pressure within the range of about 150 to about 300 p.s.i.g. The contact or residence time of the reactants in the reactor will usually be within the range of 0.1 to about hours. When maximum production of said high energy fuel comprising dimethyl bicyclodecanes is desired, it is preferred that said contact or residence time be at least 0.5 hour.

In the hydrocarbon :feed stream to said isomerization process the volume ratio of normal hexane to methylcyclopentane is usually about 3.5 to l. However, in the practice of the invention said ratio can vary -within wide limits, for example, from 1:1 to 5: 1.

The catalysts employed in carrying out said isomerization comprise metal halides, such as aluminum chloride, aluminum bromide, boron triuoride and the halides of such metals as zinc, tin, arsenic, antimony, zirconium, beryllium, titanium, iron, and the like. These catalysts are especially effective when present as complexes which are formed by interaction between the metal halides and hydrocarbons present in the reaction system. A particularly desirable isomerization catalyst is the complex of hydrocarbon with aluminum chloride. In addition to the catalyst it is desirable that the corresponding hydrogen halide be present in the reaction zone since this material maintains catalyst activity at a high level. The reaction rate and the conversion of the hydrocarbon feed is dependent on the amount of aluminum chloride in the aluminum chloride-hydrocarbon complex. Thus, to maintain a normal hexane conversion of about 55 percent, the catalyst complex should contain 60 to 62 percent aluminum chloride. However, the quantity of aluminum chloride in the complex can be varied over wide ranges to provide a corresponding range of feed reactant conversion. While the over-all activity of the catalyst is established by the aluminum chloride content, as stated, the presence of hydrogen chloride is required to provide a high activity. Usually the quantity of hydrogen chloride present is between about 2 and about 6 weight percent of the feed vwith about 4 weight percent being preferred. The hydrocarbon-to-catalyst ratio is also an -important factor in the isomerization reaction rate and generally this ratio is maintained between about 0.8:1 and about 1.4:.1 although ratios as high as 5 to 1 can be used if reaction temperatures are increased.

The removal of contaminants, namely benzene and sulfur, from the isomerization feed can be effected by contacting said feed with a dehydrogenated nickel catalyst and hydrogen under suitable conditions of elevated temperature, usually between about 3610 and about 500 F. Pressure does not appreciably affect the hydrogenation reaction and the actual pressure employed is established principally by the partial pressure of the hydrogen present. Usually the liquid hourly space velocity is between about 1 and about 3 cubic feet of liquid feed per cubic foot of catalyst per hour. Operation with an excess of hydrogen is preferred; therefore, it is desirable that more than the 3 mols necessary to convert each mol of benzene be present in the reaction zone. Preferably, the hydrogen concentration is such as to provide a hydrogen-tobenzene ratio of between about 4 and about 16` mols/mol.

As a result of the preceding operation benzene is hydrogenated and converted to cyclohexane, which is one of the desired products of the isomerization reaction; and the sulfur in the feed material reacts with the nickel catalyst, converting said catalyst to nickel sulfide. The latter reaction inactivates the catalyst, therefore, periodically it is necessary to withdraw and dump the spent catalyst and add fresh catalyst to the system.

The accompanying drawing is a diagrammatic flow sheet illustrating the various embodiments of the invention. In said drawing, all pumps, coolers, heaters, condensers, etc., have been omitted in order to simplify the explanation thereof. However, it is to be understood that the process of the invention includes such auxiliary equipment of this type which is necessary for the operation thereof and, in addition, includes the apparatus necessary to provide reflux to the top of each fractionating tower and heat to the bottom of each fractionating tower, which heat and reux are necessary for the separations being carried out in the various fractionation towers.

Referring now to said drawing, the `invention will be more fully explained. A feed stream of a mixture of hydrocarbons comprising normal hexane and methylcyclopentane, vfrom a source not shown and after being puriiiedbyhydrogenation as described above, is passed via conduit 10 through dehydrator 11 wherein substantially all the moisture present in said feed stream is rcmoved. Normally two dehydrators are operated in parallel with one dehydrator being in operation while 4the other dehydrator is being regenerated or being emptied and filled with fresh drying agent. Any suitable drying agent can be employed. However, bauxite is usually preferred. The dried :feed stream is passed via conduit 12 and one or more of the inlets shown at the various elevations, into aluminum chloride saturator 13. ln said separator A13 said feed stream contacts powdered aluminum chloride which is picked up and carried with the feed through conduits 14, 16 and 17 into isomerization reactor 18. If desired, the amount of fresh aluminum chloride suspended in said feed stream can be controlled by passing a portion or all of said feed stream through conduit 19 into said conduit 1'6 instead of passing said feed stream through said aluminum chloride saturator 13. Before entering said reactor 18, the catalyst concentration or the feed is increased by the addition of aluminum chloride-hydrocarbon complex catalyst from conduit 21 and settler 22.

The aluminum chloride-hydrocarbon complex catalyst can be originally prepared by mixing aluminum chloride and kerosene in a weight ratio of about 8:5. During operation of the process, the original complex catalyst is replaced with complex catalyst formed in the process and which contains aluminum chloride and hydrocarbon in a weight ratio of about 1:11. The viscosity of the catalyst is usually maintained at about 200 to about 350 centipoises at F. The viscosity of the catalyst can be controlled by controlling the amount of make-up aluminum chloride added Ifrom aluminum chloride saturator 13. Hydrogen chloride is added to said reactor 18 via conduit 23` from a source to be described hereinafter.

Two of the principal reactions which take place in the reactor are the isomerization of normal hexane to 2- methylpentane and the isomerization of methylcyclopentane to cyclohexane. Three other isomers of normal hexane, i.e., neohexane, diisopropyl and 3-methylpentane are also formed in varying quantities In addition, the

dimethyl bicyclodecanes product of the process, and some other higher boiling materials described hereinafter, are also formed by reactions not presently completely understood.

The etlluent from reactor comprisinlg unreacted normal hexane, unreacted methylcyclopentane, cyclohexane, said various isohexanes, said dimethyl bicyclodecanes and said other higher boiling hydrocarbons, is passed via conduit 24- into settler 2.2 whereinthe major portion of the catalyst complex is separated from the hydrocarbon material. The :major portion of the separated or settled catalyst complex is returned via conduits v2,1 and 17 to said reactor 18 as previously described.. Inasrnuch as the catalyst complex gradually loses its activity, it is desirable that a por-tion thereof be either periodically or continuously withdrawn from the system. For this purpose, a baille is provided in one end of settler 22 and separated catalyst complex can be withdrawn from said settler via conduit 216.

Although a substantial separation of catalyst complex and hydrocarbon is effected in settler 22, the hydrocarbon layer still contains some finely divided suspended catalyst complex and a major proportion of the hydrogen chloride. Said hydrocarbon layer is withdrawn from settler 22` via conduit 27 and introduced into the upper portion of coalescer 2S. Said coalescer 28 contains a bed of particulate material such as anthracite coal, ceramic chips, Raschig rings, bauxite, etc., which provides a surface for the entrained and suspended finely divided aluminum chloride hydrocarbon complex catalyst to coalesce on. Although only one coalesocr 28 has been shown in the drawing, it will be understood that two or more such coalescers can be operated in parallel similarly as described above in connection with dehydrator 11. It is also within the scope of the process to employ two or more coalescers in series. Coalesced catalyst complex collects in the bottom of coalescer 28 and is withdrawn therefrom via conduit 29.

Said hydrocarbon layer, now essentially free of entrained catalyst complex, is passed via conduit 31 into surge tank 32. Makeup hydrogen chloride can be introduced into the system via conduit 33 from a source not shown. The hydrocarbon stream in said feed surge tank 32 is passed via conduit 34 into HCl stripper 36 wherein substantially all of the hydrogen chloride is separated from said hydrocarbons. The overhead stream from said HCl stripper 36 is a hydrogen chloride rich stream which, as previously described, is passed via conduit 23 in-to isomerization reactor 18.

Bottoms product from said HC1 stripper 36 is removed therefrom via conduit 37 and introduced into caustic washer 38 wherein remaining traces of hydrogen chloride are neutralized. The caustic washed hydrocarbon product is then passed via conduit 39 into sand tower 41 which contains a bed of sand, or other similar particulate material, to remove entrained caustic which can be removed from said tower 41 via conduit 42. Although only `one sand tower 41 has been shown, two lor more such towers can be employed in parallel in the manner described above in con-nection with dehydrator 11 so as to provide for continuous operation. From said sand tower 41 the hydrocarbon stream is passed via conduit 43, feed surge tank 44 and conduit 46 into deisohexanizer tower 47. In said tower 47, said hydrocarbons are fractionated and a stream comprising the ixohexanes product of the process is removed overhead via conduit 48. The remaining hydrocarbons or bottoms product from said tower 47 is passed via conduit 49, feed surge tank 51 and conduit 52 into dimethylcyclopentanizer 53. In said tower 53, said hydrocarbons are vagain fractionated and a stream comprising unreacted normal hexane and unreacted methylcyclopentane is removed overhead via conduit 54 and recycled to conduit for rein-troduction into reactor 18 as previously described. Bottoms product from said tower 53 is passed via conduit 56, feed surge tank 57 and conduit is removed overhead via conduit 67.

6 58 into decyclohexanizer tower 59. In said tower 59, said hydrocarbons are lfractionated and a stream consisting essentially of the cyclohexane product of the process is withdrawn overhead via conduit 61. The bottoms product from said tower 59, i.e., the heavy rejectV stream of -higher boiling hydrocarbons from lche process -is passed from said tower 59 via conduit 62, feed surge tank 63 and conduit 64 into fractionator tower 66. iIn said tower 66, the hydrocarbons are fractionated and a stream cornprising cyclohexane, isoheptanes, C7, C2 and C9 naphthenes Said overhead stream in conduit 67 can -be removed via conduit 68 as a by-product of the process if desired. However, in a preferred embodiment of the invention said overhead stream in conduit 67 is passed via either conduits 69 and 17 into reactor 18, or through conduit 71 for introduction into conduit 10 for ultimate introduction into said reactor 18. As described above, the introduction of said ovenhead stream from conduit 67 into reactor 18 increases the production of saiddimethyl bicyclodecanes.

From said fractionator 66 there can be removed as a bottoms product via conduit 72 a stream boiling within the range of about 380 to about 470 F. Said stream in conduit 72 comprises dimethyl hicyclodecanes and is one of the high energy fuel products of the process of the invention. If desired, there can be removed from said fractionator 66 via conduit 73 a side stream boiling within the range of about 400 to about 430 F. and consisting essentially of ldimethyl bicyclodecanes. Said side stream is a presently preferred high energy fuel product of the process of the invention.

The fractionation of the heavy reject stream of hydrocarbons from decyclohexanizer 59 to recover the high energy fuels of the invention has been illustrated' as being carried out in a single fractionator 66 to simplify the drawing. IIf desired or necessary, said fractionation can be carried out in more than one fractionator. Any suitable fractionation system can be employed -to recover the high energy fuel products of the invention.

Similarly, the various fractionation towers 47, 53, and 59 can comprise more than one tower in actual practice if ldesired or necessary to effect the indicated separations.

As indicated above, one of the -high energy fuel products of the invention is a mixture of hydrocarbons boiling within the range of about 380 to about 470 F. and comprising dimethyl bicyclodecanes. This product, indicated in the drawing as recovered through conduit 72, has been shown by mass spectrometry analysis to be predominantly (at least 70 percent) bicyclic C12 hydrocarbons of the condensed ring type. In some instances, depending upon the fractionation system employed in fractionating the bottoms stream from decyclohexanizer 59, said high energy fuel product contains as much as V to 94 or higher volume percent of said C12 hydrocarbons.

When a high energy fuel of exceptional purity and uniformity of performance is desired the high energy fuel of the invention boiling within the range of about 400 to about 430? F. is the preferred fuel. This product, indicated in the drawing as being recovered through conduit 73, has been shown by distillation and spectral analytical methods to be a mixture of hydrocarbons containing at least and up to 99 volume percent or more of said bicyclic C12 hydrocarbons of the condensed ring type. Other analytical data set forth hereinafter show said hydrocarbons to be C12H22 hydrocarbons, i.e., dimethyl bicyclodecanes. Said preferred high energy fuel of the invention thus consists essentially of said dimethyl hicyclodecanes.

Said high energy fuel of the invention boiling within the range of about380 to about 470 F. comprises said dimethyl bicyclodecanes and usually also contains other lower boiling and higher boiling hydrocarbons. Examples of `said other hydrocarbons which can be present in amounts ranging from a trace to appreciable include, among others, the following, l-ethyl-cis-bicyclo-[4.4.0]-

1,3-dimethy1-4 butylcyclopentane; and 1,2,3,4 tetra-V methylcyclohexane.

The following examples will serve to further illustrate the invention.

EXAMPLE I This example is provided as an illustration of one embodiment of the invention on a comercial scale.

lsomerzaton Reactor Cyclohexane Isoheptanes 1-1, dimethylcyclopentane(+) 0.3

Temperatures F. Hydrocarbon feed to reactor 80 Reactor eflluent 140 HCl stripper- Top 150 Bottom 355 Pressures P.s.i.g. Reactor 155 Coalescer 40 HC1 stripper (bottom) 190 Sand tower 153 Product Fractonation Flows Gal. day Feed to desohexanizer 413,340

Compositiond Vol. percent n-Hexane 28.5 Methylcyclopentane 4.1 Cyelohexane 17.1 Isohexanes 49.6 Isoheptanes 0.2 1-1, dimethylcyclopentane(-i-) 0.5

Gah/day Deisohexanzer overhead 238,040

Composition- Vol. percent n-Hexane 17.2 Isohexanes 82.4 Methylcyclopentane 0.3 Cyclohexane 0.1 Feed to demethylcyclopentanizer 175,300

Composition* Vol. percent n-Hexane 44.1

Methylcyclopentane 9.3 Cyelohexane 40.2 Isohexanes 4.8 Isoheptanes 0.5 1-1, dimethylcyclopentane(+) 1.1 Demethyleyclopentanizer overhead (to isomerization unit) 108,400

Composition- Vol. percent n-Hexane 71.3

Methylcyclopeutane Isohexanes Cyclohexane Isolieptanes Flows: Gat/day Feed to decyclohexanizer 66,900

Composition- Vol, percent Cyclohexane 96.0 Methylcyclopentane 0.1 Isoheptanes 1.0 1-1, dimethylcyclopentane(+) 2.9 Cyclohexane product 65,130

Compositlon- Vol. percent Cyclohexane 98.1 Isoheptanes 1.0 Methylcyclopentane 0.1 1-1, dimethylcyclopentane(|) 0.8 Feed to fractionator 66 1,770

Composition- Vol. percent Cyclohexanc 21 Isoheptanes 21 C7 naphthenes 12 Cs and Co naphthenes 15 Dimethyl blcyclodecanes(l)- 31 Overhead from Fractionator 66 1,220

Composition- Vol. percent Cyclohcxane 30 Isoheptanes 30 C1 naphthenes 18 Cs and Co naphthenes 22 High energy fuel 550 Composition- Vol. percent Dimethyl bicyclodeeanes 94 Heavy ends 6 Temperatures: F Feed to delsohexanizer 240 De1sohexanizer Top 200 Bottom 255 Demethylcyelopentanzer- Top 225 Bottom 265 Decyclohexanizer- Top 258 Bottom 305 Fractionator 66- Top 400 Bottom 450 Pressures P.s.l.g. Deisohexanlzer 40 Demethylcyclopentanizer 40 Decyclohexanizer 40 Fractionator 66 5 EXAMPLE II This example is provided as 1an illustration of a preferred embodiment of the invention on a commercial scale. In this embodiment of the invention, as illustrated in the drawing, the overhead stream from fractionator 66 is recycled to reactor 18 along with the overhead from fractionator 53.

lsom erz'zaton Reactor Flows GaL/day Hydrocarbon feed to reactor 424,200

Composition- Vol. percent n-Hexane 62.0

Methylcyclopentane 17.8

Cyclohexane Isohexanes Isoheptanes 2.0 AlCu-complex catalyst to reactor 306,000 HC1 (recycle) to reactor 22,000 Reactor euent 750,800

Composition Vol. percent n-Hexane 15.8

Methylcyclopentane 2.3 Cyclohexane 9.5 Isohexanes 27.7

Catalyst 40.8 HC1 2.7

Isohcptaues( 1.2

Temperatures: F.

Hydrocarbon `feed to reactor Reactor etluent HCl stripper- Top Bottom 355 9 Pressures p sig, Reactor 155 Coalescer 40 HC1 stripper 190 Sand towers 153 Product Fractonalon Flows Gal./ day Feed to deisohexauizer 421,270

Composition- Vol. percent n-Hexane 28.6

Methylcyclopentane Cyclohexane Isohexanes Isoheptanes( l) Deisohexanizer overhead 236,965

Composition- Vol. percent n-Hexane 17.1

Isohexanes 82.5

Methylcyclopentane 0.2 Cyclohexane 0.2

Feed to demethylcyclopentanizer 184,305

Composition- Vol. percent n-Hexane 43.2

Methylcyclopentane Cyclohexane Isohexanes Isoheptanes -l) Demethylcyclopentanizer overhead 112,455

Composition- Vol. percent n-Hexane 70.9

Methylcyclopentane Isoliexanes Cyclohexane Isoheptanes Feed to decyclohexanizer 71,850

Composltonn Vol. percent Cyeloheirane` 90.6 Methylcyclopentane 0.3 Isoheptanes 1.3 C7 naphthenes 2.6 Cs and Co naphthenes 3.3 Dimethyl bicyclodecanes(+) 1.9 Cyclohexane product 65,620

Composition- Vol. percent Cyclohexane 98.5 Isoheptanes 1.0 ll/Iethylcyclopentane 0.4 Heavy ends 0.1 Feed to fractionator 66 6,230

Composition- Vol. percent Cyclohexane 6.4 Isoheptanes 4.1 C7 naphthenes 29.5 C8 and C9 naphthenes 38.4 Dimethyl bicyclodecanes 21.6 Overhead 'from fractionator 66 4,880

Composition- Vol. percent Cyclohexane Isoheptanes 42 C1 naphthenes 23 Cs'and C naphthenes 30` High energy fuel 1,350

Composition- Vol. percent Dimethyl bcyclodecanes 90 Heavy ends 10 Temperatures F. Feed to deisohexanizer 250 Deisohexanizer'- 'lop 200 Bottom 270 Demethylcyelopentanizer- Top 205 Bottom 285 Decyclohexanzer- Top 258 Bottom 330 Fractionator 66 Top 400 Bottom 485 10 Pressures: P.s.1.g. Delsohexanizer 40 Demethylcyclopentanizer 40 Deeyclohexanzer 40 Fractionator 66 5 A comparison of the above Examples I and Il shows that in Example I 550 gallons per day of high energy fuel is recovered Whereas in Example II 1,350 gallons per day of high energy fuel is recovered. Thus, recycle of the overhead stream from fractionator 66 to reactor 18 has resulted in an increase in production of high energy fuel of 800 gallons per day. Since all other operating conditions Were essentially the same in `said Examples I and II, the increase in production of high energy fuel is presently believed to be due to the presence of the C7, C8, and C9 hydrocarbons in said recycle stream. The action of said C7, `C8 and `C9 hydrocarbons in forming or promoting the formation of the dimethyl bicyclodecanes is not presently known.

It will be noted that said C7, C8 and C9 hydrocarbons comprise about one percent of the total hydrocarbon charge to the reactor. Smaller and larger amounts of said hydrocarbons can be recycled or furnished to said reactor as a part of the fresh feed. It is presently preferred that the amount of said hydrocarbons included in the feed stream to said reactor be within the range of about 0.3 to about 5 volume percent of the hydrocarbon feed stream, more preferably Within the range of about 0.5 to about 3 volume percent.

The composition of said recycle stream from fractionator 66 can vary Within rather Wide limits. For example, the amount of cyclohexane can vary Within the range of about 3 -to about 35 voluxne percent, the amount of the isoheptanes can vary Within the range of about 10 to about 50 volume percent, the amo-unt of C7 naphthenes can vary Within the range of about l0 to about 40 volume percent, and the amount of C8 and C9 naphthenes can vary Within the range of about 10 to about 50 volume percent. It is presently preferred that the C7, C8 and C9 hydrocarbons comprise at least 75'volurne percent of said recycle stream. It is also presently preferred that at least 50 volume percent of said recycle stream be C7, C8 and C9 naphthenes. The above 4ranges also apply with respect to said C7, C8 land C9 hydrocarbons when they Iare supplied from a source other than said recycle stream.

Y EXAMPLE 'In A sample of a high energy fuel prepared in accordance with the invention, and having a boiling range of 381 to 469 F., with 90 percent boiling in the range of 401 to 420 F., was analyzed by mass spectrometry. The follow- `ing results were obtained:

lEXAMPLE. 1V

A sample of the heavy reject stream of higher boiling hydrocarbons from an isomerization process being roperated generally in accordance with the method of Example l, and comparable to that illustrated in the drawing as being Withdrawn from fractionator 59 .through conduit 62, was fractionated employing a l-inch by 6-foot column packed with 9/3g inch stainless steel helices. The reiiux ratio was 60 to l.

Said sample Was fractionated into 219 fractions of about 0.4 to 0.5 volume percent of the sample charged. The results of this fractionation from fraction 181 to the end, together with tests on said fractions, are tabulated in Table lI below. The kettle product (KP) Was l percent of the original charge. Said fractions 181 to 219 contained the high energy fuel of the invention.

TABLE I Head Specific Fraction No. Temp., F. LV Percent Refractive Gravity,

@ 760 mm. Overhead Index, 20/D 20/4" C.

llc

EXAMPLE V Cuts 200 and 201 from the distillation set forth in Example IV were combined and analyzed. The following results were obtained.

Molecular weight 166.4 Carbon-hydrogen analysis, wt. percent:

Found- Carbon 86.9 Hydrogen 13.3 Calculated for C12H22 Carbon 8.67 Hydrogen 13.3 Boiling point, F. 424 Specific gravity, /4 0.8534 Refractive index, 20/D 1.4640

EXAMPLE VI The heat of combustion for Cut No. 191 and Cut NJ. 214 from the distillation set forth in Example IV were determined. The following results were obtained.

Heat of combustion, Btu.

Cut N0: per gallon (gross) clude, among others, isopropylcyclohexane and 1,3,S-trimethylcyclohexane.

While certain embodiments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto. Various other modifications of the invention will be apparent to those skilled in the art in view of the above disclosure. Such modifications are within the scope and spirit of the invention.

I claim:

1. IIn a process for the conversion of hydrocarbons wherein: a hydrocarbon feed stream comprising normal hexane and methylcyclopentane is contacted in a reaction zone with a metal halide-hydrocarbon complex catalyst under isomerizing conditions whereby at least a portion of said normal hexane is isomerized to isohexanes and at least a portion of said methylcyclopentane is isomerized to cyclohexane; and hydrocarbon eluent from said reaction zone is passed through a series of fractionation zones to separate a stream comprising isohexanes, a stream comprising a mixture of unreacted normal hexane and unreacted methylcyclopentane, a stream comprising cyclohexane and a reject stream of higher boiling hydrocarbons formed during said isomerization, the improvement which comprises fractionating said reject stream of higher boiling hydrocarbons to recover therefrom a high energy fuel comprising dimethyl bicyclodecanes substantially free of other compounds formed during said isomerization.

2. The process of claim l wherein: said isomerizing conditions include, a temperature Within the range of 9() to 160 F., a pressure within the range of 150 to 300 p.s.i.g., a contact time within the range of 0.1 to 5 hours, and a hydrocarbon-to-catalyst ratio of between about 0.5 and about 3; and said metal halide is aluminum chloride.

3. In a process for the conversion of hydrocarbons wherein: a hydrocarbon feed stream comprising normal hexane and methylcyclopentane is contacted in a reaction zone with a metal halide-hydrocarbon complex catalyst under isomerizing conditions whereby at least a portion of said normal hexane is isomerized to isohexanes and at least a portion of said methylcyclopentane is isomerized to cyclohexane; and hydrocarbon eluent from said reaction zone is passed through a series of fractionation zones to separate a stream comprising isohexanes, a stream comprising a `mixture of unreacted normal hexane and unreacted methylcyclopentane, a stream comprising cyclohexane and a reject stream of higher boiling hydrocarbons formed during said isomerization, the improvement which comprises: including in said hydrocarbon feed stream a mixture of hydrocarbons comprising isoheptanes, C7 naphthenes, CB naphthenes, and C9 naphthenes; conducting said isomerization reactions in the presence of said last mentioned mixture of hydrocarbons; and fractionating said reject stream to recover therefrom a high energy fuel comprising dimethyl bicyclodecanes, substantially free of other compounds formed during said isomerization, the yield of said high energy fuel being greater than would be obtained when said isomerization reactions are conducted in 4the absence of said mixture of hydrocarbons.

4. A process for the isomerization of hydrocarbons and the production of a high energy fuel, which process comprises in combination, the steps of: contacting a hydrocarbon feed stream comprising normal hexane, methylcyclopentane, isoheptanes, C7 naphthenes, C8 naphthenes, and C9 naphthenes with an aluminum halidehydrocarbon complex catalyst in a reaction zone at a temperature within the range of to 160 F., a pressure within the range of to 300 p.s.i.g., for a period of time within the range of 0.1 to 5 hours; passing hydrocarbon eilluent from said reaction zone to a rst fractionation zone and recovering therefrom a rst product stream comprising essentially sohexanes; passing the remainder of said hydrocarbon effluent from said first fractionation zone to a second fractionation zone and recovering therefrom a stream comprising a mixture of unreacted methylcyclopentane and unreacted normal hexane; returning said mixture of unreacted methylcyclopentane and unreacted normal hexane to said reaction zone; passing the remainder of said hydrocarbon euent from said second fractionation zone to a third fractionation zone and recovering therefrom a second product stream comprising essentially cyclohexane; passing the remainder of said hydrocarbon eluent from said third fractionation zone to a fourth fractionation zone; and recovering from said fourth fractionation zone a third product stream comprising dimethyl bicyclodecanes substantially free of other compounds formed during said isomerization and suitable for use as a jet engine fuel.

5. -ln a process for the conversion of hydrocarbons wherein: a hydrocarbon feed stream comprising normal hexane and methylcyclopentane is contacted in a reaction zone with a metal halide-hydrocarbon complex catalyst under isomerizing conditions whereby at least a portion of Said normal hexane is isomerized to isohexanes and at least a portion of said methylcyclopentane is -isomerized to cyclohexane; and hydrocarbon eduent from said reaction zone is passed through a series of fractionation zones to separation a stream comprising isohexanes, a stream comprising a mixture of unreacted normal hexane and unreacted methylcyolopentane, a stream comprising cyclohexane and a reject stream of higher boiling hydrocarbons formed during said isomerization, the improvement which comprises: fractionating said reject stream of higher boiling hydrocarbons to recover therefrom (1) a high energy fuel comprising dimethyl bicyclodecanes substantially free of other compounds formed during said isomerization and'(2) another vstream comprising isoheptanes, C7 naphthenes, C8 naphthenes and C9 naphthenes; returning said another stream to said reaction zone; conducting said isomerization reactions in the presence of said returned another stream; and recovering a greater yield of said high energy fuel by said fractionation of said reject stream than would be recovered when said isomerization reactions are conducted in the absence of said returned another stream.

6. The process of claim wherein: said isomerizing conditions include, a temperature within the range of 90 to 160 F., a pressure within the range of 150 to 300 p.s.i.g., a contact time within the range of 0.1 to 5 hours, and a hydrocarbon-to-catalyst ratio of between about 0.5 and about 3; and said metal halide is aluminum chloride.

7. A process for the isomerization of hydrocarbons and the production of a high energy fuel, which process comprises, in combination, the steps of: contacting a hydrocarbon feed stream comprising normal hexane and methylcyclopentane with an aluminum halide-hydrocarbon complex catalyst in a reaction zone at a temperature Within the range of to 160 F., a pressure within the range of to 300 p.s.i.g., for a period of time Within the range of 0-.1 to 5 hours; passing hydrocarbon etlluent from said reaction zone to a rst fractionating zone and recovering therefrom a first product stream comprising essentially isohexanes; passing the remainder of said hydrocarbon effluent from said rst fractionation zone to a Isecond fractionation zone and recovering therefrom a stream comprising a mixture of unreacted methylcyclopentane and unreacted normal hexane; returning said mixture of unreacted methylcyclopentane and unreacted normal hexane to said reaction zone; passing the remainder of said hydrocarbon eluent from said second fractionation zone to a third fractionation zone and recovering therefrom a second product stream comprising essentially cyclohexane; passing the remainder of said hydrocarbon eluent from said third fractionation zone to a fourth fractionation zone; recovering from said fourth fractionation zone a third product stream comprising dimethyl bicyclodecanes substantially free of other compounds formed during said isomerization and suitable for use as a high energy fuel, and another stream comprising cyclohexane, isoheptanes, C7 naphthenes, C8 napthenes and C9 naphthenes; recycling said another stream to said reaction zone; and carrying out said contacting of said hydrocarbon feed stream in the presence of said recycled another stream so as to increase the production of said third product stream comprising dimethyl bicyclodecanes.

8. The process of claim 7 wherein said Itemperature is within the range of 150 to 160 F., and said period of time is at least 30 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 2,415,066 Ross et al. Ian. 28, 1947 2,668,865 Schneider Feb. 19, 1954 2,953,606 Dean et al. Sept. 20, 1960 2,999,890 Davison Sept. 12, 1961 OTHER REFERENCES Conn et al.: .'.A.C.S., vol. 76, pp. 4578-80 (1954). Schneider: J.A.C.S., vol. 76, pp. 4938-45 (1954). 

1. IN A PROCESS FOR THE CONVERSION OF HYDROCARBONS WHEREIN: A HYDROCARBON FEED STREAM COMPRISING NORMAL HEXANE AND METHYLCYCLOPENTANE IS CONTACTED IN A REACTION ZONE WITH A METAL HALIDE-HYDROCARBON COMPLEX CATALYST UNDER ISOMERIZING CONDITIONS WHEREBY AT LEAST A PORTION OF SAID NORMAL HEXANE IS ISOMERIZED TO ISOHEXANES AND AT LAST A PORTION OF SAID METHYLCYCLOPENTANE IS ISOMERIZED TO CYCLOHEXANE; AND HYDROCARBON EFFLUENT FROM SAID REACTION ZONE IS PASSED THROUGH A SERIES OF FRACTIONATION ZONES TO SEPARATE A STREAM COMPRISING ISOHEXANES, A STREAM COMPRISING AMIXTURE OF UNREACTED NORMAL HEXANE AND UNREACTED METHYLCYCLOPENTANE, A STREAM COMPRISING CYCLOHEXANE AND A REJECT STREAM OF HIGHER BOILING HYDROCARBONS FORMED DURING SAID ISOMERIZATION, THE IMPROVEMENT WHICH COMPRISES FRACTIONATING SAID REJECT STREAM OF HIGHER BOILING HYDROCARBONS TO RECOVER THEREFROM A HIGH ENERGY FUEL COMPRISING DIMETHYL BICYCLODECANES SUBSTANTIALLY FREE OF OTHER COMPOUNDS FORMED DURING SAID ISOMERIZATION. 